Below, Jennifer Vail shares five key insights from her new book, Friction: A Biography.
Jennifer is a tribologist. Tribology is the science of interacting surfaces in relative motion. She is the founder of DuPont’s first tribology research lab and a member of the senior leadership team at TA Instruments. Her TED Talk, “The Science of Friction,” has been viewed more than two million times.
What’s the big idea?
We’re taught to treat friction like a nuisance—something to minimize, ignore, or design away. But this so-called enemy is quietly responsible for some of our biggest breakthroughs, from more efficient cars to insights into dark matter and human disease. The real problem isn’t friction itself, but what we miss when we stop paying attention to it.
1. Rethink the antagonist.
Friction is not something we generally have a positive association with. As a force, it opposes motion and dissipates the energy of motion. It is resistance, it works against us, it slows us down. Not a great reputation builder. Physics students always start by “ignoring friction” to simplify the problem being worked on. This further engrains into us that friction is a nuisance, both complicated and a pain.
It may be complicated, but to classify friction as an antagonist is a mistake. It’s all about perspective and objectively framing the situation you are in. If we’re driving and need to brake, friction is absolutely our hero. However, even moving the car forward requires friction. Without friction between the tire and the road, the tire would just spin around without creating the traction required to push the car forward. By writing off friction as our enemy, we miss opportunities that exist when we embrace it.
Even in situations where we want to reduce or minimize friction, clever solutions have been born from its exploration. Some are ubiquitous to everyday life, like WD-40. We have developed coatings that can withstand extreme environments, like space, so that parts can move more efficiently even in the presence of punishing temperatures and radiation. Stoppers in syringes have been designed to have just enough friction to stay put until pressed, but have low enough friction to plunge easily and smoothly during an injection. From wheels to hunting dark matter, this so-called antagonist has certainly done a lot to move us forward.
2. Challenge the status quo.
A lot of great minds found themselves deep-diving into friction, which is a testament to its importance. A common theme among them was determination in understanding the world around them, even when this meant causing societal pushback. Their efforts advanced our understanding of friction and have kept us from being at a literal standstill with motion.
Among the many titles he holds, Leonardo da Vinci is one of the founders of tribology and is renowned for his relentless curiosity. He pushed against widely held medical and scientific beliefs. His turn as a tribologist stemmed from the many machines he worked on inventing, including the pursuit of a perpetual motion machine—a widely sought-after invention throughout history. Da Vinci, however, concluded that it would be impossible to achieve, thanks to friction. He developed the first tribometers, instruments to study friction. His notebooks contain sketches of these tribometers and detail his results, leading to some of our laws of friction. He knew that friction didn’t depend on the size of an object, but its weight mattered. He could put a giant, light-weight block on a table, and it could require less force to move than a small, heavy block. He realized there were ways to lower friction, but ultimately, friction was always present. A perpetual motion machine was a fruitless pursuit.
“He realized there were ways to lower friction, but ultimately, friction was always present.”
Da Vinci is hardly the only renegade in the story of friction. Galileo’s discovery of inertia is key to our journey in understanding friction. Galileo was so good at challenging the status quo that he eventually found himself charged with heresy. But Galileo’s scientific ideas were correct. Inertia was critical to explaining why Earth can remain in constant motion, orbiting the sun in a heliocentric universe, without us noticing or feeling it. Newton would later document this as the First Law of Motion.
You could say that those studying friction tended to rub the status quo the wrong way. Osborne Reynolds would redefine our understanding of how fluids flow. Heinrich Hertz, over his Christmas break one year, would boggle minds by explaining how even glass spheres would deform when in contact under an imposed load and then return to their original shape, a type of behavior previously only considered with softer, springier materials.
3. Communication is the key to innovation.
Da Vinci may have been our first tribologist, but his work was largely unknown until recent times. Despite his meticulous note-taking, he didn’t publish his findings. His notebooks were largely undiscovered until centuries later, with the last notebooks being found as late as the 1960s. The first laws of friction wouldn’t become public knowledge for 200 years after Da Vinci, when Guillame Amontons essentially redid the same work in the 17th century. Amontons was also inspired by perpetual motion. Fortunately for science, Amontons did share his results.
Other discoveries in the world of friction tell the same tale. A fluid’s resistance to flow, its internal friction, was studied by a Frenchman named Poiseuille and separately, by a German engineer named Hagen. Poiseuille is the far more famous of these two men, with the unit of viscosity named after him. A famous equation relating viscosity to flow rate and pressure was referred to as “Poiseuille’s equation” for years, simply because he published in more widely known media than Hagen, who shared the same findings. This work was done in 1839. Hagen wouldn’t be widely recognized until the 1920s.
“A lot of great minds found themselves deep-diving into friction, which is a testament to its importance.”
And in the 20th century, the same would happen with another significant fluid study. In tribology, there’s something known as a Stribeck curve. It’s used to understand the friction in lubricated machine parts under different loads, speeds, and fluid viscosities. It’s named after German Richard Stribeck, even though similar work was done decades earlier by his fellow German, Adolf Martens. Innovation is only half the battle. Communicating what you’ve discovered is just as important.
4. Embrace the small things.
Sometimes, incremental improvements are frowned upon. We want big, mind-blowing leaps. We should always embrace progress, including incremental progress.
A 2011 study found that nearly one-third of the fuel we were putting in cars was being spent to overcome friction. If we remove necessary friction, like the braking and tire friction mentioned earlier, the waste on friction was around 20 percent. Since 2011, the fuel efficiency of internal combustion engine vehicles has improved steadily, despite cars becoming larger and more powerful. This is due to incremental improvements lowering the friction in cars.
When you multiply the effects across the number of cars and trucks on the roads, it’s estimated that tribological improvements could save almost 300 million tons of CO2 emissions over five years. That amounts to just shy of one percent of global annual emissions. That’s a big deal, so never underestimate the power of small changes.
5. Don’t ignore what you can’t see.
If you did ignore friction, as we are taught to do as students, everything we design would fail. Forces are invisible, but just because you can’t see them, it doesn’t mean they aren’t there. Beyond simply being a part of the physics that makes our world work, acknowledging the invisible allows us to uncover answers to some of our biggest unsolved scientific mysteries.
A team from The Education University of Hong Kong found indirect evidence of dark matter surrounding black holes simply by factoring friction into their work. They were studying the orbits of two different stars that are each companion stars to black holes. The orbits were decaying, meaning that eventually the black holes would consume the stars. When the teams calculated the decay rate, their results were significantly smaller than the actual measured decay rate. Once they factored in a type of friction called dynamical friction, the calculation was spot on. This dynamical friction would be caused by the dark matter surrounding the black holes. Our first indirect evidence of the dark matter surrounding black holes, brought to you by not ignoring friction in the equation.
“Once they factored in a type of friction called dynamical friction, the calculation was spot on.”
Inside our own bodies, scientists have wondered what role friction plays in the folding of proteins. Proteins are the building blocks of life and are formed from chains of amino acids that fold into 3D structures. But the folding isn’t always successful, resulting in misfolded proteins that can be toxic. These misfolded proteins have been associated with diseases such as Alzheimer’s and Parkinson’s. Researchers are working to understand what causes misfolded proteins in hopes of developing better treatments and prevention strategies. To understand the misfolding, they must consider all factors, including friction. Where does the friction originate? How much does it contribute to the folding process? These are the types of questions we are seeking to answer in our quest to explore friction…and to not ignore the invisible.
Friction is not our enemy. When we approach it correctly, it’s a powerful tool that has helped us evolve as a civilization and will continue to do so.
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